Re: [PATCH v2] init/gcov: allow CONFIG_CONSTRUCTORS on UML to fix module gcov
On Wed, 2021-01-20 at 18:04 +0100, Peter Oberparleiter wrote: > > > Tested with a kernel configured with CONFIG_GCOV_KERNEL, without > > the patch nothing ever appears in /sys/kernel/debug/gcov/ (apart > > from the reset file), and with it we get the files and they work. > > Just to be sure: could you confirm that this test statement for UML also > applies to v2, i.e. that it fixes the original problem you were seeing? Yes, I tested this version too :) johannes
Re: [PATCH v2] init/gcov: allow CONFIG_CONSTRUCTORS on UML to fix module gcov
On 20.01.2021 17:20, Johannes Berg wrote: > From: Johannes Berg > > On ARCH=um, loading a module doesn't result in its constructors > getting called, which breaks module gcov since the debugfs files > are never registered. On the other hand, in-kernel constructors > have already been called by the dynamic linker, so we can't call > them again. > > Get out of this conundrum by allowing CONFIG_CONSTRUCTORS to be > selected, but avoiding the in-kernel constructor calls. > > Also remove the "if !UML" from GCOV selecting CONSTRUCTORS now, > since we really do want CONSTRUCTORS, just not kernel binary > ones. > > Signed-off-by: Johannes Berg Looks good+nicer than v1 to me! I also tested this patch on s390 and can confirm that it doesn't break gcov-kernel there. Reviewed-by: Peter Oberparleiter Andrew, do we need additional reviews/sign-offs? Could this go in via your tree? > --- > Tested with a kernel configured with CONFIG_GCOV_KERNEL, without > the patch nothing ever appears in /sys/kernel/debug/gcov/ (apart > from the reset file), and with it we get the files and they work. Just to be sure: could you confirm that this test statement for UML also applies to v2, i.e. that it fixes the original problem you were seeing? > > v2: > * special-case UML instead of splitting the CONSTRUCTORS config > --- > init/Kconfig| 1 - > init/main.c | 8 +++- > kernel/gcov/Kconfig | 2 +- > 3 files changed, 8 insertions(+), 3 deletions(-) > > diff --git a/init/Kconfig b/init/Kconfig > index b77c60f8b963..29ad68325028 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -76,7 +76,6 @@ config CC_HAS_ASM_INLINE > > config CONSTRUCTORS > bool > - depends on !UML > > config IRQ_WORK > bool > diff --git a/init/main.c b/init/main.c > index c68d784376ca..a626e78dbf06 100644 > --- a/init/main.c > +++ b/init/main.c > @@ -1066,7 +1066,13 @@ asmlinkage __visible void __init __no_sanitize_address > start_kernel(void) > /* Call all constructor functions linked into the kernel. */ > static void __init do_ctors(void) > { > -#ifdef CONFIG_CONSTRUCTORS > +/* > + * For UML, the constructors have already been called by the > + * normal setup code as it's just a normal ELF binary, so we > + * cannot do it again - but we do need CONFIG_CONSTRUCTORS > + * even on UML for modules. > + */ > +#if defined(CONFIG_CONSTRUCTORS) && !defined(CONFIG_UML) > ctor_fn_t *fn = (ctor_fn_t *) __ctors_start; > > for (; fn < (ctor_fn_t *) __ctors_end; fn++) > diff --git a/kernel/gcov/Kconfig b/kernel/gcov/Kconfig > index 3110c77230c7..f62de2dea8a3 100644 > --- a/kernel/gcov/Kconfig > +++ b/kernel/gcov/Kconfig > @@ -4,7 +4,7 @@ menu "GCOV-based kernel profiling" > config GCOV_KERNEL > bool "Enable gcov-based kernel profiling" > depends on DEBUG_FS > - select CONSTRUCTORS if !UML > + select CONSTRUCTORS > default n > help > This option enables gcov-based code profiling (e.g. for code coverage > -- Peter Oberparleiter Linux on Z Development - IBM Germany
[PATCH v2] init/gcov: allow CONFIG_CONSTRUCTORS on UML to fix module gcov
From: Johannes Berg On ARCH=um, loading a module doesn't result in its constructors getting called, which breaks module gcov since the debugfs files are never registered. On the other hand, in-kernel constructors have already been called by the dynamic linker, so we can't call them again. Get out of this conundrum by allowing CONFIG_CONSTRUCTORS to be selected, but avoiding the in-kernel constructor calls. Also remove the "if !UML" from GCOV selecting CONSTRUCTORS now, since we really do want CONSTRUCTORS, just not kernel binary ones. Signed-off-by: Johannes Berg --- Tested with a kernel configured with CONFIG_GCOV_KERNEL, without the patch nothing ever appears in /sys/kernel/debug/gcov/ (apart from the reset file), and with it we get the files and they work. v2: * special-case UML instead of splitting the CONSTRUCTORS config --- init/Kconfig| 1 - init/main.c | 8 +++- kernel/gcov/Kconfig | 2 +- 3 files changed, 8 insertions(+), 3 deletions(-) diff --git a/init/Kconfig b/init/Kconfig index b77c60f8b963..29ad68325028 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -76,7 +76,6 @@ config CC_HAS_ASM_INLINE config CONSTRUCTORS bool - depends on !UML config IRQ_WORK bool diff --git a/init/main.c b/init/main.c index c68d784376ca..a626e78dbf06 100644 --- a/init/main.c +++ b/init/main.c @@ -1066,7 +1066,13 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void) /* Call all constructor functions linked into the kernel. */ static void __init do_ctors(void) { -#ifdef CONFIG_CONSTRUCTORS +/* + * For UML, the constructors have already been called by the + * normal setup code as it's just a normal ELF binary, so we + * cannot do it again - but we do need CONFIG_CONSTRUCTORS + * even on UML for modules. + */ +#if defined(CONFIG_CONSTRUCTORS) && !defined(CONFIG_UML) ctor_fn_t *fn = (ctor_fn_t *) __ctors_start; for (; fn < (ctor_fn_t *) __ctors_end; fn++) diff --git a/kernel/gcov/Kconfig b/kernel/gcov/Kconfig index 3110c77230c7..f62de2dea8a3 100644 --- a/kernel/gcov/Kconfig +++ b/kernel/gcov/Kconfig @@ -4,7 +4,7 @@ menu "GCOV-based kernel profiling" config GCOV_KERNEL bool "Enable gcov-based kernel profiling" depends on DEBUG_FS - select CONSTRUCTORS if !UML + select CONSTRUCTORS default n help This option enables gcov-based code profiling (e.g. for code coverage -- 2.26.2